A= (x+3)(2x-1)-3x(2x+5)
=2x²-x+6x-3-6x²-15x
=-4x²-10x-3
B= (4t+1)(4t-1)-(3t+2)²
=16t²-1-(9t²+12t+4)
=16t²-1-9t²-12t-4
=7t²-12t-5
C=2(s+5)(s-5)+(4s+3)²
=2(s²-25)+16s²+24s+9
=2s²-50+16s²+24s+9
=18s²+24s-41
D=(3x+4)²-(1-2x)(6+x)
=9x²+24x+16-(6+x-12x-2x²)
=9x²+24x+16-6-x+12x+2x²
=11x²+35x+10